This invention relates to a method for electrically controlling the actuation of a reciprocating fluid (i.e. gas or liquid) pump, preferably a pump with static pumping chambers and more preferably a multi-piston fluid pump. The invention also extends to an electrically selectable hydraulic poppet valve for employment in the method.
Reciprocating multi-chamber fluid pumps are well known and generally comprise a plurality of static pumping chambers each equipped with a poppet valve to control inlet of fluid into the chamber (on an inlet stroke) for subsequent pressurisation therein on a discharge stroke. Common embodiments of reciprocating multi-chamber pump have a plurality of piston-in-cylinder modules disposed about an annular lobed cam, eccentric or swash plate, carried by a drive shaft. As the drive shaft is rotated to cause rotation of the lobed cam or eccentric, the piston-in-cylinder modules are sequentially operated to cause hydraulic fluid to be pumped from a low-pressure inlet manifold through the poppet valve in each module to a high-pressure delivery manifold. By enabling or disabling one or more of the pumping chambers (or modules), variable stepped changes in the displacement of the pump can be achieved.
One previously proposed method of disabling a piston-in-cylinder module is to hold open mechanically the inlet valve to the cylinder of the module so that the fluid drawn into the cylinder on the inlet stroke is pumped back into the low-pressure inlet manifold throughout the delivery stroke rather than to the high-pressure delivery side of the pump. In this way, for example, a pump having "n" cylinders and means to independently enable or disable each of the piston and cylinder modules, could offer "n" stepped levels of displacement. It will be appreciated that with such an arrangement, the variations in displacement are fixed depending simply on the number of piston and cylinder modules which are utilised at any one time.
Such previously proposed mechanical arrangements have significant disadvantages in that they have proved to be relatively slow and noisy in operation as well as being limited in the degree of displacement variation which can be achieved.
One aim of the present invention is to obviate or mitigate the aforesaid disadvantages. A further aim is to provide a method for the real time control of the displacement of a multi-chamber reciprocating fluid pump having individually electrically controllable poppet valves serving as inlet valves to at least some of the pumping chambers.